Dual Xeons: HT on or off?

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Vertigo Acid

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Is there any advantage to having HT enabled on a dual Xeon setup when I rarely load my system up to 100% usage on all 4 logical processors? Or does that have anything to do with why I should leave it on or turn it off?
 
Why would you want to turn it off??

Another site, don't know if their name is voodoo here or not, but tomshardware is doing another amd vs intel stress test. They are using Pentiums, but with HT activated, the Intel machine faired noticeably better.
 
I would say it's a matter of taste.

You still have only so many clock cycles - just shared between 2 or 4 logical procs.

Until more apps and games are released that take advantage of the new dual core cpus and the multi-proc systems - it's not a real benefit. It just means that you can open more apps than someone on a single CPU computer. Unless you're using video or engineering apps that will use the additional procs.

In the near future - those of us with Hyperthreading dual xeons are going to be a lot happier than the peeps with non-HT dual core procs.

We just have to wait for the software to catch up with the hardware.

Just imagine - multithreaded CS:S or BF2 :D

 
rodsfree said:
I would say it's a matter of taste.

You still have only so many clock cycles - just shared between 2 or 4 logical procs.

Until more apps and games are released that take advantage of the new dual core cpus and the multi-proc systems - it's not a real benefit. It just means that you can open more apps than someone on a single CPU computer. Unless you're using video or engineering apps that will use the additional procs.

In the near future - those of us with Hyperthreading dual xeons are going to be a lot happier than the peeps with non-HT dual core procs.

We just have to wait for the software to catch up with the hardware.

Just imagine - multithreaded CS:S or BF2 :D

Click to expand...

Dual core Opteron's will RAPE HT dual Xeon's. Xeon's don't scale as well as Opterons and don't have the same memory performance. Also, 4 physical cores will beat out two physical cores /w logical processors everytime.

Intel really needs to do something about the Xeons deficiencies. the FSB, and shared bus architecture doesn't give it enough advantage over plain desktop parts. With two CPU's crowding a limited bus, while sharing memory, each chip you add gives you less and less performance for your money. Plus, I don't think they actually beat the Opteron at anything anymore. Especially not when you get into 4 way and 8 way configurations.

I don't know if this is true or not, but someone in another thread stated, that AMD added a flag to the dual core parts, to detect software that supports HT and then use the second core for the extra threads. Therefore it should respond to any HT optimized software, but instead of having one processor and executing threads out of the single processors pipeline, the software will execute on a seperate core.
 
Bouncing off of what's been said already, you take no performance hit by enabling HT and leaving it enabled. If you already have a legally licensed OS for 4 cores, enabling HT won't cause that to be invalidated normally. It just means that on a best case scenario you could process 8 instructions at once instead of 4. But, as has been stated, the other 4 will be slightly delayed since they're running in unused sections of the chips.

My vote is leave it enabled, it won't hurt anything.
 
if your using Win2k, there might be some performance decreases with HT on.
with XP and 2003, there is no reason to have HT off.
 
Steel Chicken said:
if your using Win2k, there might be some performance decreases with HT on.
with XP and 2003, there is no reason to have HT off.
Click to expand...

Agreed, I have heard that Windows 2000 doesn't work properly with HT in some cases.
 
Sir-Fragalot said:
Agreed, I have heard that Windows 2000 doesn't work properly with HT in some cases.
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Win2K sees HT as a full on processor, which it is not. So the process scheduler tends to give it way more to do than it is capable of doing, which causes problems and slowdowns.
 
Sir-Fragalot said:
Dual core Opteron's will RAPE HT dual Xeon's. Xeon's don't scale as well as Opterons and don't have the same memory performance.
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Wasn't discussing the comparason between the 2.
Was talking about what we have currently.

Also - My 2 1.6Ghz LV HT Xeons clocked to 2.64Ghz will beat the crap out of your Opterons on a dollar per clock cycle basis.

I paid $73.00 shipped for the pair. :D

What did you pay for Operton Goodness?


 
Why dont you compare bencmarks with even a 1.6 Opteron...see how that goes, lemme know :rolleyes:
 
rodsfree said:
Wasn't discussing the comparason between the 2.
Was talking about what we have currently.

Also - My 2 1.6Ghz LV HT Xeons clocked to 2.64Ghz will beat the crap out of your Opterons on a dollar per clock cycle basis.

I paid $73.00 shipped for the pair. :D

What did you pay for Operton Goodness?


Click to expand...

Paid $500 for 2 Opteron 246's with a Tyan (2882-D) and Windows Server 2003 Enterprise. It was a bundled deal.

Pretty good bang for the buck I'd say. :cool:

I am pretty sure that even with your LV Xeon's overclocked, Opterons would still outperform them.

Physical dual cores will always outperform logical processors. HT is great, I have defended it myself many times. Still doesn't beat the physical. Dual Core Pentium-D's will have near the performance of the Xeon. Probably more so in some cases due to the ram speed advantage on the P4 Platform.
 
rodsfree said:
I would say it's a matter of taste.

You still have only so many clock cycles - just shared between 2 or 4 logical procs.
Click to expand...
Exactly, so I guess my question is, for getting the most speed for a program that is singled thread (ie games), wouldn't turning HT off give more clock cycles to that one logical processor?
 
Vertigo Acid said:
Exactly, so I guess my question is, for getting the most speed for a program that is singled thread (ie games), wouldn't turning HT off give more clock cycles to that one logical processor?
Click to expand...

Not really, HT only works when something is coded to take advantage of it. Single threaded apps like games don't bennefit from it and aren't hurt by it.
 
Vertigo Acid said:
Exactly, so I guess my question is, for getting the most speed for a program that is singled thread (ie games), wouldn't turning HT off give more clock cycles to that one logical processor?
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not at all.
 
Are we talking about xeon with ht 1.0 or 2.0? 1.0 slowed down the cpu as much as 2.0 speeded it up, if the programs didn know wdf ht was. If your xeon is below 2ghz, then it might have ht 1.0. All the lv ones have 2.0 thank god.
 
alienb said:
Why dont you compare bencmarks with even a 1.6 Opteron...see how that goes, lemme know :rolleyes:
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Quite well thank you. :D

Beats a pair of Opteron 182's - Gets close to the 252's

Also just got a pair of 1.6LV's that clock to 3.44Ghz stable enough to boot WinXP but fault on Prime95.

That's 4 chips for less than the cost of 1 Opteron.

Even with the Tech Tour bundles.
 
alienb said:
Why dont you compare bencmarks with even a 1.6 Opteron...see how that goes, lemme know :rolleyes:
Click to expand...

Running SANDRAs benchmark.
These 2 1.6LV Xeons @ 2.64Ghz more than DOUBLE the scores of a 3.0Ghz Prescott.
Prime95 stable for 24hrs - on air cooling
I can post the numbers for you later - computer is at home - I'm at work.

My contention was that this thread was about XEONS and HT
Not XEON vs OPTERON.
If you want to do that dance then start another thread - I'll show up! :D

I wish that I had the spare bucks and time to do the AMD tech tour thing like Sir-Fragalot did. (I live 3 hrs from Atlanta)

I'm all about the MFLOPS and the MONEY! :D

I could care less about the Intel vs AMD rivalary.

 
rodsfree said:
My contention was that this thread was about XEONS and HT
Not XEON vs OPTERON.
If you want to do that dance then start another thread - I'll show up! :D
Click to expand...

Don't let the AMD lovers upset ya. Who gives a rat's ass which cpu scores higher in 3dmark or sandra. I'm not a big gamer so I wouldn't know much about that, but for pure workstation power NO ONE and I mean NO ONE uses AMD. Its either SGI, G4's or Xeons. You don't even have to run one of those stupid test, you can tell by simply working in a high-end app. Xeons kill all other Pentiums and AMD in this area.
 
Robstar said:
I'd leave HT off. There are known Security Issues with it under the free unixes....perhaps in windows too? I don't know.
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:rolleyes:
That's all FUD right now, the day I see a working exploit for that, that will bork over my system or lose me control, I will be worried
 
nape said:
Don't let the AMD lovers upset ya. Who gives a rat's ass which cpu scores higher in 3dmark or sandra. I'm not a big gamer so I wouldn't know much about that, but for pure workstation power NO ONE and I mean NO ONE uses AMD. Its either SGI, G4's or Xeons. You don't even have to run one of those stupid test, you can tell by simply working in a high-end app. Xeons kill all other Pentiums and AMD in this area.
Click to expand...


uhhh did you see how the movie "sin city" was made?
 
nape said:
Don't let the AMD lovers upset ya. Who gives a rat's ass which cpu scores higher in 3dmark or sandra. I'm not a big gamer so I wouldn't know much about that, but for pure workstation power NO ONE and I mean NO ONE uses AMD. Its either SGI, G4's or Xeons. You don't even have to run one of those stupid test, you can tell by simply working in a high-end app. Xeons kill all other Pentiums and AMD in this area.
Click to expand...

Check your benchmarks buddy, the Opteron kicks the crap out of the Xeon's pretty easily. In terms of memory bandwidth and bus architecture the Opteron has several advantages over the Xeon. Not to mention, the Pentium D is very competitive with the Xeon. A dual core Pentium D would be just as fast as a dual CPU Xeon if not faster due to faster memory. The Xeon uses a shared bus, just as the dual core Pentium D does. This - bottleneck. The more CPU's you add to a Xeon system the worse the scaling gets. The bus simply chokes the things.
 
extremefire said:
Why would you want to turn it off??

Another site, don't know if their name is voodoo here or not, but tomshardware is doing another amd vs intel stress test. They are using Pentiums, but with HT activated, the Intel machine faired noticeably better.
Click to expand...

Back when I used to buy Intel chips for servers, we had to disable HyperThreading for server use. It was causing SQL Server to really screw the pooch. The query plans were dramatically different for 4-way and 8-way. Since they were not real CPU's, it was really giving us headaches.
 
needles said:
Back when I used to buy Intel chips for servers, we had to disable HyperThreading for server use. It was causing SQL Server to really screw the pooch. The query plans were dramatically different for 4-way and 8-way. Since they were not real CPU's, it was really giving us headaches.
Click to expand...

I am willing to bet they were win2000 boxes
 
Going back to the original poster - what OS are you running? if this a workstation running Win 2K or Win XP - then no point in switching on HT on a dual rig - since the OS only supports 2 CPU's. Linux or Win server different matter.
 
cyberjt said:
Going back to the original poster - what OS are you running? if this a workstation running Win 2K or Win XP - then no point in switching on HT on a dual rig - since the OS only supports 2 CPU's. Linux or Win server different matter.
Click to expand...

Not true, virtual processors aren't counted as physical in Windows XP Home or Pro. Windows 2000 I am not sure about. Although I think 4 show up even then.
 
Sir-Fragalot said:
Not really, HT only works when something is coded to take advantage of it. Single threaded apps like games don't bennefit from it and aren't hurt by it.
Click to expand...

This isn't exactly correct.

The problem with processors today is that they're substantially faster than the memory they access. A HT processor works by keeping two execution states ready to go in hardware. When one execution state stalls during a fetch to memory, the other execution state is expected to be runnable and steps in to start executing the state it has.

The stall to go to memory can be so long that the other state has 400 cycles to execute without even interrupting the memory fetch from the first state.

An appplication doesn't need to be multithreaded to take advantage of HT. There just needs to be more than one runnable thread on the whole system, not just in a single application. In Windows, you might have other applications (or even the system itself) making another thread runnable, outside of your single-threaded game or application.

Further, if you look into it, most applications aren't strictly single-threaded. The problem is they don't scale well to mulitple processors, since they only schedule one runnable thread out of the many they create.

The answer to Vertigo's original question is that it depends on the applications being run on the machine. It's possible to write applications (either on purpose or by accident) that scale negatively with hyperthreading machines. If you find yourself running such an application, or such a combination of applications, you'll want to turn HT off. You'll also want to turn hyperthreading off if you're not using a HT-aware operating system.

I hope this help clarifies the issue.
 
Hyperthreading on my work desktop 2x Xeon is off because it slows down our main application, and quite a bit.

Since the gains for applications where it "works" are pretty minor I think the major advantage of Hyperthreading is that it makes things a lot smoother when one process is hammering the AGP bus and another wants CPU (this seems to be an interuptability issue and I observed it both under Linux and Windoze).

But with a dual CPU system you have that advantage anyway.
 
Sounds like I'm just going to have to do some benchies on and off and see what's faster for the apps I run and the games I play.
 
Vertigo Acid said:
Sounds like I'm just going to have to do some benchies on and off and see what's faster for the apps I run and the games I play.
Click to expand...

Post your results plz....
I'd like to know too!


 
Hyperthreading is the best thing the Netburst Architecture has going for it. I wouldnt turn it off.
 
Vertigo Acid said:
Sounds like I'm just going to have to do some benchies on and off and see what's faster for the apps I run and the games I play.
Click to expand...

Or, enumerate the apps you use and games you play. Perhaps other people have already studied the situation.
 
USMC2Hard4U said:
Hyperthreading is the best thing the Netburst Architecture has going for it. I wouldnt turn it off.
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Obviously, you've never used an application which runs slower with HT enabled!
 
mikeblas said:
Obviously, you've never used an application which runs slower with HT enabled!
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He probably hasn't....Most of the run of the mill stuff, Office and etc, wouldn't have a really noticable slow down because of HT.
I've got some engineering apps that have shown a couple of problems though.

What I'm waiting for is for all the apps and games to be multithread enabled because the new dual core chips. Right now a dual core chip doesn't really benefit anyone because most apps and games are single threaded. Same argument about why HT or multiprocessor systems don't show alot of benefit in most applications. As the new dual core chips become popular then the game and software vendors will be rewritting and patching their code to take advantage of the multithreading ability of the new cpu's and incidently it'll benefit those of us with multi-proc systems and with HT cpu's.

CS:S multithreaded on 2 1.6LV's @3.2......drool!!!!!



 
rodsfree said:
What I'm waiting for is for all the apps and games to be multithread enabled because the new dual core chips.
Click to expand...

I have to say that I am a little afraid of it.

Of course it has to be but it will mean that in addition to the usual segmentation faults, memory leaks and other technical bugs you will also get deadlocks and/or data corruption from missynchronization.

In particular in the early days when programmers are new to it. I expect a pretty bloody battle, with lots of applications that can be switched to global locks (single thread) abd lots of forum postings about which apps to run that way.

Those of us with quad CPU/core systems will probably be worst off.
 
Synchronization bugs already happen. Consumer software that abuses threads (Pinnacle Studio 7 and Studio 8 are great examples) are abundant.

There are also driver-level problems; fortunately, dual-proc systems have already tought some companies lessons about building and testing multi-threaded software.

Funny thing is, synchronization isn't a new thing. It's just that PC-class developers think they don't need to know about it.

If you start actually looking at it, I think you'll be surprised at how many applications you use that are already multi-threaded.
 
I vote for leaving HT turned on.

For my personal system I just went from Dual Xeon 3.0's (HT on) to an X2 4800+. The Xeons were definitely smoother for multitasking. This X2 is really fast though, it's just that there are some situations where you have many things going on that the Xeons chugged right along and the X2 hitches around.

Dual dual-core Opterons, however, would own everything :)
 
rolo said:
I vote for leaving HT turned on.

For my personal system I just went from Dual Xeon 3.0's (HT on) to an X2 4800+. The Xeons were definitely smoother for multitasking. This X2 is really fast though, it's just that there are some situations where you have many things going on that the Xeons chugged right along and the X2 hitches around.

Dual dual-core Opterons, however, would own everything :)
Click to expand...

After a pair of 7800GTX's that's the next planned upgrade for my box. :D Dual Core Opty smoothness.
 
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